The present invention relates to a device in linear actuators of the kind comprising an open rail or a hollow profile rail on or in, as the case may be, a carriage is guided for displacement in the longitudinal direction of the rail with the aid of a rotatable threaded spindle in screw engagement with the carriage.
More precisely, the invention concerns a device in linear actuators of the kind in which a screw support is provided at least to one side of the carriage, said screw support arranged to form a bearing supporting the spindle intermediate the points of support at the spindle ends.
A screw support of this kind is intended to prevent the threaded spindle, usually a ball bearing screw, from bending or deflecting outwards upon attainment of a so called critical r.p.m. value. Such outwards deflection depends on the length and rotational speed of the spindle. This critical value is attained at an earlier stage when the spindle is of a particularly great length and/or the rotational speed is high than in the case of short spindles or lower rotational speeds.
In linear actuators of considerable length, formed with a long spindle that operates at comparatively high r.p.m. values, it is possible to prevent the above-mentioned outwards deflection of the spindle by using one or several support bearings in the form of such screw supports. In order to allow carriage movements from one end of the linear actuator to the other, various technical solutions have been suggested to make the carriage bring along, in its movements, a screw support from a selected point of support positioned along the length of the spindle and then, upon its return movement, release and leave the screw support at the same point of support. Hitherto known locking means for interconnecting carriage and screw supports have, however, suffered from the disadvantage of being unnecessarily complicated, in addition to which they have been subjected to unnecessarily heavy wear during the translatory movements of the screw support by means of the carriage, often resulting in unsatisfactory operational reliability in the linear actuator. Generally, the space requirements of the locking means on one or both sides of the linear actuator are such that there is a risk that the screw support gets wedged on equipment disposed close to the linear actuator, a situation which likewise impairs the operational reliability of the linear actuator and which consequently may lead to breakdowns.
The invention provides a device by means of which screw supports may be brought along by the moving carriage and be secured in pre-determined places disposed along the spindle, which device is of simple structure, requires a minimum of space while at the same time it exposes the components of the device to a minimum of wear, in consequence whereof the device is imparted a considerable degree of operational reliability. The features characterizing the device in accordance with the invention appear from the appended claims.